1. Field of the Invention
The present invention relates to a recording apparatus of the type in which a magnetic fluid is held and made to protrude from a single or a plurality of recording electrodes of a magnetic metal, and a Coulomb force is applied to the end of protrusion of the magnetic fluid to make the fluid fly, thereby to effect a printing on a recording surface.
2. Description of the Prior Art
The specification of U.S. Pat. No. 4,258,371 discloses a recording apparatus making use of a magnetic fluid. This recording apparatus has a plurality of magnetized styli disposed at a predetermined pitch. A magnetic fluid is deposited to each stylus to form wave-like protrusions of the magnetic fluid on the ends of the styli along the array of the styli. A high voltage is selectively applied between the styli and control electrodes opposing to the styli to apply a Coulomb force to the end of protrusion of the magnetic fluid to make the latter fly toward the recording paper thereby to effect a printing on the recording paper by the magnetic fluid serving as an ink.
The magnetic fluid is consumed as it flies successively, so that it is necessary to make up for the shortage of the magnetic fluid. To cope with this demand, Japanese Patent Laid-open Publication Nos. 100161 and 100162/1980 disclose magnetic fluid supplying devices incorporating an elongated magnet.
In general, there is a tendency that, in the magnetic fluid placed in a magnetic field as shown in FIG. 1, the magnetite in the fluid is attracted by the magnet so that the density of the magnetite becomes higher in the portion of the fluid closer to the magnet than in the portion remoter from the magnet.
In the case where the recording portion 1 of the recording apparatus is connected to a fluid tank 2 by means of an elongated magnet 3 as shown in FIG. 2, the concentrated magnetic fluid 4 around the magnet is strongly magnetized by the magnet and is pulled by a strong force to have an inertia to move upwardly as indicated by an arrow A overcoming the force of gravity. On the other hand, the portion of the magnetic fluid 4 remote from the magnet, in which the density of the magnetite is comparatively low, is magnetized by the magnet not so strongly that only a small upward force is generated. In consequence, this portion of the magnetic fluid 4 tends to move downwardly as indicated by an arrow B. As this phenomenon takes place over the entire length of the magnet 3, the magnetic fluid held by the upper portion of the magnet 3 is progressively condensed while the magnetic fluid on the lower part of the magnet is thinned gradually.
In the recording portion of the apparatus, therefore, the density of the magnetite in the magnetic fluid becomes considerably high as compared with the initial density, so that the extent of magnetization of the magnetic fluid 4 becomes higher. This causes a change in the form of protrusion of the magnetic fluid from the expected form, as well as an increase of the viscosity of the magnetic fluid. In consequence, the flying characteristics of the magnetic fluid 4 during recording are degraded, and the fluidity of the ink, i.e. magnetic fluid, is deteriorated to hinder the recording.